I think that's false, with the current state of internet, advertising everywhere, enshitification and monetization of users private data, some people are ready to pay for services that were considered "free".

I am paying for kagi, and I would pay for a good, private browser (I know they make onion but I'm on linux, not macos or windows).

But I'm not pitching a browser. This is a web security product which people do pay for - it's a billion dollar product category in fact. The only functional difference is that the malware and fraud protection it provides is demonstrably superior to all of its competitors.